The present invention relates to a wavelength stabilizing light source apparatus for stabilizing the oscillation wavelength of the light emitted by a light source such as a semiconductor laser, the apparatus being additionally equipped with an optical path length difference forming device.
Of various light sources, semiconductor laser devices have received widespread acceptance as a coherent light source in many fields. Because the oscillation wavelength of a semiconductor laser is highly susceptible to the fluctuations in temperature and inrush current, such fluctuations need to be minimized wherever the semiconductor laser device is used.
One conventional way to minimize the fluctuations in temperature and injection current is to equip the semiconductor laser device with an electronic heating and cooling device such as a Peltier device as well as with a temperature detector such as a thermistor to measure the temperature of the semiconductor laser device. In operation, the Peltier device is driven by the signal output from the thermistor so as to keep constant the temperature of the semiconductor laser device. Under a more precise stabilizing method of the prior art called an external feedback method, there is provided an etalon plate setup and/or an atomic and molecular absorption line arrangement stipulating a wavelength reference. Differences with respect to the wavelength reference are represented by error signals that are fed back to the semiconductor laser device where the temperature and inrush current are corrected accordingly to stabilize the oscillation wavelength.
One disadvantage of the above wavelength reference-based stabilizing device is that it tends to be large in scale and thus expensive. With this kind of device, the precision of wavelength stabilization depends on the bandwidth of the detection characteristic in effect when error signals are detected as well as on the accuracy of peak value detection.